Air pressure control system



Jan. 5, 1960 c. M. OLEARY 2,919,910

AIR PRESSURE CONTROL SYSTEM Filed June 3, 1958 I 2 Sheets-Sheet 1Cape/.55 4/. 0254?) 1 N VEN TOR.

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irraeA/fy United States Patent AIR PRESSURE CONTROL SYSTEM Charles M.OLeary, Los Angeles, Calif.

Application June 3, 1958, Serial No. 739,499

14 Claims. (Cl. 267-1) This invention relates to air balanced oil wellpumping units and more particularly to maintaining the balancingpressure of the air balancing system in step with the varying loadsimposed on the air balancing unit due to changes in well loadconditions, which will require an addition or reduction of air pressureto the balancing system, to maintain the well load in relatively perfectbalance under varying well load conditions.

It is well known to those in the art of oil well pumping, that slugs ofwater enter the well bore and must be pumped to the surface, and thatwater is heavier than oil, which increases the counter-balance load.When the water slug is removed, gas moves in and lightens thecounter-balance load, or the fluid flow to the well bore may be inspasmodic amounts of the mixture of oil and gas which aflects the wellload. 1 All of the preceding conditions are variable and change fromtime to time during the pumping operations As an example, the gaspressure increases and decreases with the tides in the coastal areas.Also, the water flow into the well bore increases with the oceans meanhigh and mean low tide. Many other factors, too numerous to mention,influence the well counter-balancing loadings.

It will be noted that when the well load builds up above the normalbalancing pressure that the time cycle between the up and down-stroke ofthe well pumper changes, making a longer time period on the up-stroke ofthe air-balancing unit; and when the'well load is light, the time cycleis faster on the up-stroke than on the down-stroke.

When the Well load is nearly perfectly balanced, the time cycle betweenthe up and down-strokes are approximately equal.

It is also well known in the art of air counter balancing of oil wellpumping units, that the air pressure in the system is higher at thebottom of the pumping stroke than at the top of the stroke. "Thispressure variance can be as much as 60 p.s.i. between the up anddownstrokes of the air balancing systems air pressure.

An object of this invention is to provide a fluid responsive devicewhich is affected by the pressure buildup and pressure drop time cyclebetween the up and down strokes of the air-balanced pumping unitscounterbalancing systems pressure changes.

A further object of this invention is to provide a time cycle fluidresponsive device that will release air pressure from the balancingsystem when the down stroke exceeds a predetermined time cycle and tobuild up pressure in the system when the up stroke time cycle dropsbelow a predetermined time cycle.

It is an object of this invention to maintain the time cycle between theup and down strokes of the pumping unit as nearly equal as possible.

It is an object of this invention to relieve the prime mover of thepumping unit, .the belt drive and gear box, as Well as all of theassociated parts from overload conditions by controlling thecounterbalance forces in step with the varying well-load changes at alltimes.

2,919,910 Patented Jan. 5 1960 An object of this invention is to,provide acompletely automatic, infinitely variable pressure controlsystem for air balanced oil well pumping units, wherein the balancingpressures range from 100 p.s.i. to as much as 500 p.s.i.

Figure l is a fragmentary side elevation view of an air balance oil wellpumping unit partially in section and partially in elevation with partsof the pumping unit eliminated from the drawings for brevity, but arewellknown to those in the art. The pitman head bearing 4 is attached tothe walking beam 1, and is pivotly connected to pitman arm 8, which ispivotly connected to a crank arm, not shown, and a speed reducer alsonot shown, to produce a reciprocating motion to walking beam '1, whenthe crank, not shown, is rotated as is well known in the art. Thebalance cylinder beam bearing 12, is bolted to walking beam 1. Cylinderhead 20 is connected to the walking beam 1 by connector pin 16,

which forms a pivotal connection between the walking beam 1, the airbalancing cylinder 32, and air receiver clamping flange 22. This permitsthe air balance cylinder 32, air receiver 24 and clamping flange 22,which is fixedly attached to air balance cylinder 32, to move verticallywith the oscillatory motion of the walking beam 1.

Air balance piston assembly 40, as shown, is in air balance cylinder 32,and is fixedly attached to hollow piston rod 4'4, which rests upon fixedbase 60, and is pivotly associated therewith through piston rod ballpivot 56. The piston 40, and piston rod 44, which is pivotally mountedon the fixed base 60, forms a closure for the lower end of the airbalance cylinder 32, except for fluid passages which will hereinafter bedescribed. As stated, air balance piston assembly 40 forms the lowerclosure for the air balance cylinder 32. Cylinder head 2i? forms theupper closure for air balance cylinder 32.

Air ports 28 are provided at the upper end of air balance cylinder 32,to pass air freely to and from air balance cylinder 32 to air receiver24.

The upper end of the air balance piston assembly 40 is provided withhollow piston rod air ports 36, which withdrawing air pressure from thebalancing systems air receiver 24 and balance cylinder 32, throughpassage described.

Air passage 68 is threaded and receives air line 72. Air line 72 isthreaded at its opposite end and is screwed into pipe cross 76. Theupper end of pipe cross 76 receives vertical pipe line 80 which isthreaded thereto. The upper end of pipe line 80 is threaded and connectsto pipe elbow 89, into which pipe line 88 is threaded. The opposite endof pipe line 88 is threaded to receive check valve 92 which opens towardthe hollow piston rod 44. Pipe line 96 is threaded to check valve 92 atone end and connected by threaded means to air compressorltlll. Aircompressor 100 is driven by electric motor 1% by suitable belts andpulleys as indicated at 103. 112 indicates a power source for electricmotor Til-t and 12d indicates a starting switch for electric motor 104.

Power line 116 is from the power source 112 to starting switch 12a) backto electric motor 134. Power line 12a is from starting switch 124 toswitch 128. In the system, a manual switch, not shown, is provided toinitially build up air pressure in the system, before oil pumpingoperations are started.

The switch 123 is provided with an actuator stem 132, and is spaced fromswitch actuator stem 136 which projects from double-acting diaphragmhousing 140. The diaphragm extension stem 144 which projects from theopposite end of double-acting diaphragm housing 140 carries a reduceddiameter 138 which is spaced from the pressure release mechanism of theunloader valve 148. The double-acting diaphragm housing 140 consists oftwo halves, 3G0 and 304, which are separated by diaphragm member 212.

From the pipe cross 76 a pipe line 156 is provided, which, at one end,is threaded into pipe cross '76, and at the other end into pressurevolume control valve 160. It will be noted that the pressure volumecontrol valve 160 may be used as a fully opened and fully closed valveor may be used as a fluid flow modulator valve, depending upon thedampening effect of the fluid flow desired to be maintained, in the airpressure control system.

Extending from the pressure volume control valve 16% is pipe line T64which is threaded at one end to valve res and at the other end to elbow168, into which is also threaded pipe line 172 which at one end isthreaded into elbow 176. A nipple 192 connects elbow 176 to pipe T 18%which, when valve 160 is in the open position, provides an open fluidflow passage from the air balancing systems pressure fluctuations.Extending from pipe T 186 are two pressure lines, 188 and 184, whichconnect directly into the double acting diaphragm housing 1%, intohousing sections 300 at 200, and housing section 3% at 1% through fluidports 276 and 280 as shown in the drawings. it will be noted thatpressure line 188 is a coiled section and that pressure line 134 is alsocoiled and, further, that the number of coils in line 188 are fewer thanthe number of coils in line 184. Now referring directly to the coils T88and 184, the said coils are of drawn tubing of very small diameter,approximately one to two-thousandths of an inch internal diameter, orlarger in diameter if necessary. The length and internal diametersprovide a dampening effect, the fluid flow resister eflect dependingupon the internal diameter and the lengths of the fluid resister tubes1% and 184 which connect into the double acting diaphragm housing 140and diaphragm housings 300 and 304 as stated above.

In Figure 2 or" the drawings, a cross section of the double actingdiaphragm housing 140 is shown. The double acting diaphragm housing 140consists of two dished housings, 34M) and 304, which are separated fromeach other by the flexible diaphragm member 212. A series of bolts, 272,clamp the dished housings 3% and 3&4, to the flexible diaphragm member2122, resulting in forming two separate pressure chambers, as indicatedat 28-1 and 288 in the drawings. The pressure chamber 234 is providedwith a fluid passage 276, which permits fluid pressure to either flowinto or discharge from the chamber 284, through connector 260 andresistor line 188. Also the pressure chamber 288 is provided with afluid passage 28% which permits fluid pressure to either flow into ordischarge from the chamber 288 through the connector 196 and resistorline 184.

The flexible diaphragm 212 has a central passage as indicated at 221.The diaphragms actuator stern fits snugly into the passage 221. Thediaphragm actuator stem 258 is threaded as indicated at 227. Thediaphragm plates, 216 and 217, slip over the threaded portions ofactuator stem 228 and are clamped to the flexible diaphragm member 212by the diaphragm piston rod clamping bolts 22@.

The diaphragm actuator stem 228 is provided with two extensions, 13-6and 144, which are smaller in diameter than the threaded portion of thediaphragm actuator stem 22%. The said small diameter extension 136passes through the dished housing sea as indicated at 136, in thedrawings, and is sealed by 0 ring is dished housing 3 3i). Also thesmaller diameter extension 144 passes through the dished housing 3%, asindicated at 144 in the drawings, and is sealed by O ring 292 in dishedhousing 304-. Opposite the extension 136 of the diaphragm actuator stem228, which projects beyond the dished housing 3'90, is provided anelectric switch 128, and its actuator stem 132, which is spaced from thesaid stem 136. It will be noted that the electric switch 123 is in thenormally ofl position; also that the flexible diaphragm member of thedouble acting diaphragm is in its neutral position. The diaphragmextension 144 of the diaphragm actuator stem 2% which projects beyondthe dished housing 3M and carries a second reduced diameter as indicatedat 138. The outermost end of said extension 1133 in the neutral positionof the flexible diaphragm 212 is spaced from the pressure relief valve24-4 in pressure relief valve housing 143.

Pipe line 1:32 is threaded at both ends, one end of which is threadedinto pipe T 76 and the other into the pressure relief valve 148 which,when in an open posi tion, releases air from the balancing system, aswill be more fully described.

The pressure reliet valve housing 148 contains chamber 2 55 and a fluiddischarge port 256 which, at one end, communicates with chamber 261which is ported at 260 to the atmosphere. The chamber 261 is also portedat 26 3- to receive check valve actuator stem 138.

The said fluid discharge port 256 forms a ball check valve seat inchamber 245 as indicated at 252. A ball check valve 244 is shown in aseated position and is held seated by ball check valve spring 248 whichabuts to the bushing The pressure relief valve housing 148 carries athreaded bushing 24% which is ported at 251, as indicated in thedrawings, which screws into the pressure relief valve housing into thethreaded bushing 2% is threaded pressure line 152, the opposite end ofwhich is threaded into pipe '5'- 76, and forms an unobstructedcommunication from the air receiver 24, balance cylinder 32 and hollowpiston rod 44.

The operation of the device and all related structure is as follows:Assume that the air pressure is supplied to the closed system fluidreceiving unit by the air or fluid supply source, which is the aircompressor 1%, electric motor W4 and all related structure. The airpressure build-up comes under the isothermal compression formula betweenthe balance cylinder 32, the air receiver 24, the piping between checkvalve 92, in the air pressure supply line to the balancing cylinder 32,and the air line supplying air pressure to the double acting diaphragmhousing 3 through the pressure volume control valve 16h up to the pipe T1%.

The pressure volume control valve res monitors, meters, or controls theflow of air to the restrictor lines 384 and This monitoring ismaintained when air flows to or from the restrictor lines 184 and 183.In other words, the pressure volume control valve provides a cushion forthe restrictor lines 184 and 188. it is possible to leave the valve Milout of the system, but it is preferred to have it in, for the reasonthat it could provide, in the absence of any other function, a cut offvalve.

Furtherv the fluid restriction lines 1134 and 138 are limited to a verysmall internal diameter of two to three thousandths of an inch, whichproduces a high frictional flow resistance in either direction of airflow.

Assume the walking beam 1 was making 20 strokes per minute. This wouldallow only 1.52 seconds for the 5 down stroke and 1.48 seconds to reachits maximum low pressure. Therefore, if the up and down time incrementsare relatively equal, the pressure in the diaphragm chambers 284 and 288is relatively constant. The time cycle between the up and down strokesis not suflicient to provide any appreciable pressure change in eitherof the chambers. If the time cycle on the down stroke is materiallylonger than on the up stroke this would be an indication of the airbalancing unit being over counter balanced. In this instance, a greatervolume of air will be delivered to the diaphragm chamber 284 throughfluid restrictor line 188, due to its shorter length it provides asmaller magnitude of fluid pressure resistance than through restrictorline 184. In other words, if the down stroke of the walking beam and allthe attached equipment is longer than the up stroke, then an airpressurehas been established in the air receiver 24 for a longer periodof time. As a result of this increased time, the air pressure backsthrough the system until it reaches the restrictor lines 184 and 188.Due to the fact that line 188 has a smaller resistance than line 184,more air passes into chamber 284. This increase in pressure in chamber284 deforms the diaphragm in the direction of valve 148. When thepressure in chamber 284 becomes great enough the stem extension 138 onthe end 144 of stem 228 is urged against the spring loaded ball check244. This unseats the ball check 244. Unseating the ball check releasessome of the pressure in the system.

The released air pressure now passes from the air receiver 24 throughthe ports 36, in the piston assembly 40,

through the hollow piston rod 44, the port 68, pipe 72,

pipe cross 76, pipe 152, and out opening 260. When sufficient pressurehas been released the time cycle be tween the up and down strokesassumes a more equal condition. This permits the excess air that is inchamber 284 to return to the system through the restrictor line 188 andthe diaphragm resumes its normal form which results in releasing thestem extension 138 from engagement with the ball check valve 244.

It may be seen, after the above description, that a greater volume ofair will be delivered to chamber 284 than to chamber 288. As a result ofthe diflerential of time in the time cycles, between the up and downstrokes, airin chamber 284 cannot flow out as fast as it entered. Thiscauses an air pressure build up in chamber 284.

The pressure build up in chamber 288 is slower to reach the time cyclechange due to the greater length of the fluid restrictor line 184. Thedifference in the time period permits the increased pressure in thediaphragm chamber 284 to flex or deform the diaphragm 212. Deforming thediaphragm urges the diaphragm stem 228 toward the unloader valve 148 torelease air pressure from the air balancing system to establish arelatively equal up and down stroke time cycle.

Now, assuming the wall load is under counter balanced, the walking beamon the down stroke drops faster due to the reduced resistance of thelower pressure in the balancing system which unloads the prime mover. Onthe up stroke, the load is heavier due to the under counter balancing ofthe load. 4

Now considering the time cycle of the up stroke, which is greater nowthan on the down, air passes into the air receiver 24 for a longerlength of time than it passes from the receiver. As before stated, theair compressor is in the normally off position. Since the entire systemis closed and there has initially been a pressure build up that wasequal, particularly in the chambers 284 and 288, air to the receiver 24must be obtained from the system. When the up stroke is of a greaterlength of time than the down stroke, air is permitted to pass from thechambers 284 and 288 for a greater length of time. Due to v the factthat fluid restrictor line 188 has a smaller magnitude of fluid pressureresistance than line 184, air is permitted to pass from chamber 284 in agreater volume than from chamber 288. The result of this is that theexcess pressure in chamber 288 deforms or flexes the diaphragm 212toward switch 128. End 136 of the stem 228 engages the plunger 132 ofthe switch which results in closing the electrical circuit to actuatethe air compressor 100. Actuation of the compressor results in puttingair into the system. Until such time as the pressure build up in thesystems air counter balancing unit reaches a point where the time cyclebetween the up and down strokes again become relatively equal, at whichtime the flexible diaphragm 212 moves to its neutral position movingstem 136 away from switch actuator stem 132 deactivating electric motor104 and air compressor 100.

The diaphragm chamber 288 and its restrictor line 184 which are indirect communication with the air balancing system forms a mean averagepressure chamber. The diaphragm chamber 284 also forms a mean averagepressure chamber when the time cycles between the up and down strokes ofthe well pumping unit are relatively equal. However, the diaphragmchamber 284 is-more responsive to well load conditions and the pressuretherein will not represent the mean average pressure when the time cyclebetween the up and down strokes changes, which will cause the flexiblediaphragm 212 to move in one direction or the other, to either releaseor build up air pressure in the air balancing system.

In the final summation of the operation of the fully automatic,infinitely variable, pressure control system for air balanced oil wellpumping units, wherein the balancing air pressures range from p.s.i. forshallow Wells up to 500 p.s.i. for extremely deep wells, this unitrequires no adjustments or modification between the air pressure rangeshereinbefore set forth. The magnitude of the fluid restrictor lines 188and 184 are of such length and proportion as to provide an infinitelyvariable time cycle pressure control to the double acting diaphragmmember to maintain the time cycle between the up and down strokes of anair balanced oil pumper relatively constant, regardless of the welldepth and the required air balancing pressure.

-It is also to be understood that the electric switch 128 may besubstituted with an air pressure control valve to actuate an aircompressor not electrically driven.

While in order to comply with the statute, the invention hasbeendescribed in language more or less specific as to structuralfeatures, it is to be understood that the invention is not limited tothe specific features shown, but that the means and construction hereindisclosed comprises a preferred form of putting the invention intoeffect, and the invention is therefore claimed in any of its forms ormodifications within the legitimate and valid scopeof the appendedclaims.

What is claimed is:

1. In an air pressure control system having a fluid supply source and anormally pressurized closed fluctuating reciprocating fluid receivingunit, connected to said source; a fluid pressure control system betweenand connected to said source and unit comprising a housing; a switch andvalve actuating resilient means in said housing that divides the latterinto a pair of chambers; an element extending outwardly of each chamberand connected to said means; fiuid flow restrictor structure connectedto said housing and in communication with each chamber; a fluid carryingconduit connected to said source, said unit and said restrictorstructure; mechanism associated with one element to actuate said fluidsource and mechanism associated with the opposed element to relievepressure in said unit.

2. In an air pressure control system having a fluid supply source and anormally fluctuating pressurized closed system reciprocating fluidreceiving unit, connected to said source; a fluid pressure controlsystem between and connected to said source and unit comprising ahousing; a switch and valve actuating resilient means in said housingthat divides the latter into a pair of chambers; an element extendingoutwardly of each chamber and connected to said means; fluid flowrestrictor structure connected to said housing and in communication witheach chamber; a fluid carrying conduit connected to said source, saidunit and said restrictor structure; mechanism associated with oneelement to actuate said fluid source and mechanism associated with theopposed element to relieve pressure in said unit; said resilient meansbeing a diaphragm.

3. In an air pressure control system having a fluid supply source and anormally fluctuating pressurized closed system reciprocating fluidreceiving unit, connected to said source; a fluid pressure controlsystem between and connected to said source and unit comprising ahousing; a switch and valve actuating resilient means in said housingthat divides the latter into a pair of chambers; an element extendingoutwardly of each chamber and connected to said means; fluid flowrestrictor structure connected to said housing and in communication witheach chamber; a fluid carrying conduit connected to said source, saidunit and said restrictor structure; mechanism associated with oneelement to actuate said fluid source and mechanism associated with theopposed element to relieve pressure in said unit; said structurecomprising at least one fluid resistance carrying tube.

4. In an air pressure control system having a fluid supply source and anormally fluctuating pressurized closed system reciprocating fluidreceiving unit, connected to said source; a fluid pressure controlsystem between and connected to said source and unit comprising ahousing; a switch and valve actuating resilient means in said housingthat divides the latter into a pair of chambers; an element extendingoutwardly of each chamber and connected to said means; fluid flowrestrictor structure connected to said housing and in communication witheach chamber; a fluid carrying conduit connected to said source, saidunit and said restrictor structure; mechanism associated with oneelement to actuate said fluid source and mechanism associated with theopposed element to relieve pressure in said unit; said structurecomprising a pair of coiled fluid carrying tubes.

5. In an air pressure control system having a fluid supply source and anormally fluctuating pressurized closed system reciprocating fluidreceiving unit and connected to said source; a fluid pressure controlsystem between and connected to said source and unit comprising ahousing; a switch and valve actuating resilient means in said housingthat divides the latter into a pair of chambers; an element extendingoutwardly of each chamber and connected to said means; fluid flowrestrictor structure connected to said housing and in communication witheach chamber; a fluid carrying conduit connected to said source, saidunit and said restrictor structure; mechanism associated with oneelement to actuate said fluid source and mechanism associated with theopposed element to relieve pressure in said unit; said structurecomprising a pair of restrictor fluid carrying tubes, interconnected tosaid pair of chambers, one of which has a greater magnitude of fluidpressure restriction than the other.

6. An air pressure control system having a fluid supply source and anormally pressurized closed system reciprocating fluid receiving unit,connected to said source; a fluid pressure control system between andconnected to said source and unit comprising a housing; a switch andvalve actuating resilient means in said housing that divides the latterinto a pair of chambers; an element extending outwardly of each chamberand connected to said means; fluid flow restrictor structure connectedto said housing and in communication with each chamber; a fluid carryingconduit connected to said source, said unit and said restrictorstructure; mechanism associated with one element to actuate said fluidsource and mechanism associated with the opposed element to relievepressure in said unit; said mechanism comprising a switch to actuatesaid fluid source.

7. In a differential air pressure control system having a fluid supplysource and a normally pressurized closed system reciprocating fluidreceiving unit, connected to said source; a fluid pressure controlsystem between and connected to said source and unit comprising ahousing; a switch and valve actuating resilient means in said housingthat divides the latter into a pair of chambers; an element extendingoutwardly of each chamber and connected to said means; fluid flowrestrictor structure connected to said housing and in communication witheach chamber; a fluid carrying conduit connected to said source, saidunit and said restrictor structure; mechanism associated with oneelement to actuate said fluid source and mechanism associated with theopposed element to relieve pressure in said unit; said second mentionedmechanism comprising a ball check valve.

8. A time cycle control mechanism for air balanced oil well pumpingunits comprising two separate pressure chambers of relatively equalvolume, the said two separate pressure chambers being separated by aflexible diaphragm member; a piston member fixedly attached to saidflexible diaphragm and extending through and beyond said pressurechambers; a pressure release mechanism spaced from one end of saidpiston member on one side of said piston extension; a pressure build upmechanism spaced from the other end of said piston; 21 pair of fluidflow resistor lines communicating with the interior of each of saidpressure chambers at one end and communicating at the other end with thepressure within the said air balancing system, said fluid flow resistorlines having difierent fluid flow characteristics from each other,operable upon a change between the time cycle between the up and downstrokes of said air balanced oil pumping unit to cause movement of saidpiston member to either release pressure from said air balance system orto build up pressure in air balance system.

9. In an air pressure control system having a fluid supply source and anormally pressurized closed fluctuating reciprocating fluid receivingunit, connected to said source; a fluid pressure control system betweenand connected to said source and unit comprising a housing; a switch andvalve actuating resilient means in said housing that divides the latterinto a pair of chambers; an element extending outwardly of each chamberand connected to said means; fluid flow restrictor structure connectedto said housing and in communication with each chamber; a fluid carryingconduit connected to said source, said unit and said restrictorstructure; mechanism associated with one element to actuate said fluidsource and mechanism associated with the opposed element to relievepressure in said unit; said elements being switch and valve actuatingextensions.

10. In an air pressure control system having a fluid supply source and anormally pressurized closed fluctuating reciprocating fluid receivingunit, connected to said source; a fluid pressure control system betweenand connected to said source and unit comprising a housing; a switch andvalve actuating resilient means in said housing that divides the latterinto a pair of chambers; an element extending outwardly of each chamberand connected to said means; fluid flow restrictor structure connectedto said housing and in communication with each chamber; a fluid carryingconduit connected to said source, said unit and said restrictorstructure; mechanism associated with one element to actuate said fluidsource and mechanism associated with the opposed element to relievepressure in said unit; said resilient means and structure comprising adiaphragm and a pair of coiled fluid carrying tubes respectively.

11. In an air pressure control system having a fluid supply source and anormally pressurized closed fluctuating reciprocating fluid receivingunit, connected to said source; a fluid pressure control system betweenand connected to said source and unit comprising a housing; a switch andvalve actuating resilient means in said housing that divides the latterinto a pair of chambers; an element extending outwardly of each chamberand connected to said means; fluid flow restrictor structure connectedto said housing and in communication with each chamher; a fluid carryingconduit connected to said source, said unit and said restrictorstructure; mechanism associated with one element to actuate said fluidsource and mechanism associated with the opposed element to re lievepressure in said unit; said resilient means and elements comprising adiaphragm and a switch and valve actuating extensions respectively.

12. In an air pressure control system having a fluid supply source and anormally pressurized closed fluctuating reciprocating-fluid receivingunit, connected to said source; a fluid pressure control system betweenand connected to said source and unit comprising a housing; a switch andvalve actuating resilient means in said housing that divides the latterinto a pair of chambers; an element extending outwardly of each chamberand connected to said means; fluid flow restrictor structure connectedto said housing and in communication with each chamber; a fluid carryingconduit connected to said source, said unit and said restrictorstructure; mechanism associated with one element to actuate said fluidsource and mechanism associated with the opposed element to relievepressure in said unit; said resilient means and structure comprising adiaphragm and a pair of coiled fluid carrying tubes respectively.

13. In an air pressure control system having a fluid supply source and anormally pressurized closed fluctuating reciprocating fluid receivingunit, connected to said source; a fluid pressure control system betweenand connected to said source and unit comprising a housing; a switch andvalve actuating resilient means in said housing that divides the latterinto a pair of chambers; an element extending outwardly of each chamberand connected to said means; fluid flow restrictor structure connectedto said housing and in communication with each chamber; a fluid carryingconduit connected to said source, said unit and said restrictorstructure; mechanism associated with one element to actuate said fluidsource and mechanism associated with the opposed element to relievepressure in said unit; said resilient means and structure comprising adiaphragm and a pair of restrictor fluid carrying tubes, interconnectedto said pair of chambers, one of which has a greater magnitude of fluidpressure restriction than the other respectively.

14. In an air pressure control system having a fluid supply source and anormally pressurized closed fluctuating reciprocating fluid receivingunit, connected to said source; a fluid pressure control system betweenand connected to said source and unit comprising a housing; a switch andvalve actuating resilient means in said housing that divides the latterinto a pair of chambers; an element extending outwardly of each chamberand connected to said means; fluid flow restrictor structure con--nected to said housing and in communication with each chamber; a fluidcarrying conduit connected to said source, said unit and said restrictorstructure; mechanism associated with one element to actuate said fluidsource and mechanism associated with the opposed element to relievepressure in said unit; said resilient means and mechanism comprising adiaphragm and a switch to actuate said fluid source respectively.

References Cited in the file of this patent UNITED STATES PATENTS

